The correct conclusion you can draw about the level of economic development in a country where most workers are in the tertiary and quaternary sectors is:
Countries in which most workers are in these sectors typically have a high level of economic development.
This is because the tertiary (services) and quaternary (knowledge-based) sectors are often associated with advanced economies, where a significant focus is placed on services, technology, and information rather than agriculture or manufacturing, which are typical of less developed economies.